In a wireless charging system, a wireless charging mat wirelessly transmits power to an electronic device that is placed on the mat. The electronic device has a receiving coil and rectifier circuitry for receiving wireless alternating-current (AC) power from a coil in the wireless charging mat that is in the proximity of the receiving coil. The rectifier converts the received AC power into direct-current (DC) power. When there is a foreign object on the mat, the mat control circuitry may take suitable actions to prevent undesirable heating.